In a prior U.S. Pat. No. 4,476,514, it is taught that maintaining a degree of ionization in the atmosphere of work spaces results in neutralization of unwanted electric charges, and it discloses apparatus for accomplishing this. Spaced pairs of insulated conductors maintained at high positive and negative voltages with respect to ground are suspended near the ceiling of a work space, and the conductor pairs are equipped with ionizing points to emit positive and negative ions into the atmosphere.
Further experience has made it evident that it is desirable to maintain a certain degree of ionization in the air at bench top level, and a co-pending application Ser. No. 550,688, filed Nov. 10, 1983, and assigned to the assignee of the present application, discloses apparatus for determining the ambient electric field at any desired location. This enables automatic control of the ionization apparatus to maintain ionization at a desired state.
Measuring apparatus of the sort described in the '688 application, when mounted on a bench top, or on a wall at bench top level, is subject to accidental physical damage, and is also subject to momentary electrical effects due to the charges on persons moving near or past the apparatus, to cause undesired variation of the ionization equipment. It has been found, for example, that when this sensing device is located near a conveyor belt, objects moving on the belt past the ion sensing device possess sufficient charges to cause undesired adjustment of the ion generation equipment.
To observe or monitor the level of ionization of the air in a large work space would, however, require either the use of a large number of the measuring devices, or transportation of a measuring device about the space for use at various locations. I have discovered a method and apparatus by which a single measuring device can be used to give an indication of ionization conditions at bench level throughout a large space.
Various advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and objects attained by its use, reference should be had to the drawings which form a further part hereof, and to the accompanying descriptive manner, in which there is illustrated and described a preferred embodiment of the invention.